Manufacture of photographic emulsions



June 25, 1935. ARENs 2,005,837

MANUFACTURE OF PHOTOGRAPHIC EMULSIONS Filed July 1, 1952 in van for 5 5y Afforne y UNITED STATES PATENT OFFICE MANUFACTURE OF PHOTOGRAPHIO EMULSIONS Hans Arena, Dessau in Anlialt, Germany, asaignor to Agra Ansco Corporation, Bingliamton, N. Y., a corporation of New York Application July 1,1932, Serial No. 620,483 In Germany July I, 1931 8 Claims. (Cl. 95-7) My present invention relates to silver halide substances which cause fog are, for instance. silver gelatin l ion layers, nitrate, the known photographic ripening sub- One of its objects is to provide a process of stances, for instance, products of decomposition manufacturing such emulsions which after deof vegetable or animal proteins prepared by alveloping directly give positives. Another obkaline or alkaline fermentative hydrolysis and 5 ject are the emulsions directly yielding positives a simultaneous partial oxidation (cf. U. S. Patwhich show no fog at the places of highest illumient No. 1,719,711) or proteins prepared by acid nation. Reference is made to the accompanyhydrolysis and simultaneous partial oxidation ing drawing which illustrates the gradation curve (cf. U. S. Patent No. 1,815,983) or thiazole com- 10 of an emulsion as obtainable by my invention. pounds (cf. U. S. Patent No. 1,725,934), or mix- 10 As is known the blackening of a light-sensitures of these compounds, furthermore reducing tive photographic silver halide emulsion layer compounds such as developing substances, for reaches, with an increasing illumination, a maxiinstance, hydroquinone, paraphenylendiamine, mum value and then diminishes again. In that amidol which are preferably used in admixture 5 part of the gradation curve which lies beyond with ripening substances. The substances may the apex and which is named the solarization be added to the emulsion in the emulsifying procregion, the density, in spite of further increasess or in an after-treatment which is preferably ing the illumination is progressively diminished. .carried out after washing the emulsion. It has It has already been proposed preliminarily to proved advantageous to heat the emulsion. II

expose, for the preparation of direct positives, a the emulsion is heated to ahigh temperature heat- 20 silver halide emulsion layer, previous to the proping can be shortened and if the emulsion is heated er exposure, until the solarization limit is obto a lower temperature the heating operation tained, so that by the subsequent exposure the must be carried on for a prolonged time, for.innuclei capable of development uniformly prostance, when heating the emulsion to 100" C.

duced in the whole layer are made insensitive the duration will be about half an hour, how- 2 to development in picture-forming gradation. ever, when heating the emulsion only to 45 C. However, such an emulsion layer which has been heating must be continued for about 20 to 24 subjected to preliminary exposure, is of no prachours. When incorporating in the emulsion an tical value, because it has an insuflicient gradaexcess of silver nitrate there ispreferably used tion, i. e. a too flat gradation, because of the an excess of ammonia; if there is no excessof 30 application of the preliminary exposure on comammonia present the emulsions must be heated mercial scale is associated with great diiliculties. for a longer time and eventually to a higher This invention is based on the observation that temperature. When using the above enumerated by causing a strong fog on a silver halide emulripening substances the excess of ammonia may sion and bringing the emulsion thus prepared be omitted without the necessity of heating the ,35 to strong solarization (by heating the fogged emulsion longer or to a higher temperature for emulsion to a high temperature for a short time this reason. The substances are added while disor to a lower temperature for a longer time) solved in a suitable solvent; in most cases wayields an emulsion which is suitable for the diter will do. If a finished emulsion, that is an rect production of positives by exposure and deemulsion that has already been washed, is to 40 velopment. This result is attained by the addibe subjected to the treatment according-to this tion to the emulsion of substances, which cause invention a solution of one or more of the said fog whereby a solarization curve is obtainable substances is added to the emulsion ready for the course of which is similar to that of the being cast and finely distributed therein. The normal gradation curve. These substances have emulsion is then heated as already described. It 5 the property of forming nuclei capable of demay be pointed out that not all finished emulvelopment in the emulsion in an extent which sions give the same good results but all emulsions corresponds with the formation of such nuclei which after a preliminary exposure show a. suit- 1 by exposure to light of the emulsion until the able solarization curve will and are made with a w-apex' of the gradation curve is reached, that is weakly ripening gelatin show at least the same 'when adding said substances in a sufllcient quangood solarization curve when treated according tity that they cause a fog which corresponds to my process. with the maximum blackening of an usual emul- The following examples serve to illustrate my sion that amounts, for instance, to the value 3 invention. measured by the Martens sensitometer. Suitable Example 1.In this example there is instanced 55 the manufacture of an emulsion showing a good solarization curve. The following three solutions are prepared for this purpose:

Solution 1 10 grams of gelatin 46 cc.:of a 10 percent solution of bromide 3 cc. of a 10 per cent solution of potassium iodide 50 cc. of water ammonium Solution 2 100 cc. of a 10 per cent solution of silver nitrate.

to which so much of a 25 per cent solution'of ammonia has been added that the precipitating silver hydroxide is again dissolved g Solution 3 10 grams of gelatin I 34 cc. of a 10 per cent solution of ammonium bromide 1 cc. of a '10 per cent solution of potassium iodide 15 cc. of water These solutions are mixed by first heating So lutions 1 and 2 to about 80 C.'and then adding Solution 1 to Solution 2. This mixture is kept at about 90 C. for about /2 hour. Hereafter Solution 3 is heated to about 80 C. and added to the mixture of Solutions 1 and 2. Heating is still continued for about '6 minutes, whereupon the whole is cooled. The hardened emulsion is then washed and worked up as usual. In casting 6 cc. of a 10 per cent solution of ammonium bromide may be added'to the'emulsion. The operation is carried out in an open vessel so that the ammonia can partially evaporate during heating. Example 2.An emulsion which shows a good.

solarization curve is prepared, for instance, by means of aweakly ripening gelatin, as follows:

To 100 cc. of a solution containing 10 per cent of gelatin there were added 8 grams of ammonium bromide and 0.3 gram of potassium iodide. To this solution there was added at a temperature of 43 C. 100 cc. of an ammoniacal solution containing 10 per cent of silver nitrate heated rather quickly and the emulsion was ripened at 45 C. After half an hour 10 grams of dry gelatin reduced to small pieces were added. The emulsion is washed with water and then molten To the molten emulsion there is added one of the known ripening substances, for instance, to 1 kilo of emulsion 10 milligrams of gelatin treated as fol-.

lows: 2.6 grams of gelatin are boiled with 0.2 gram of colloidal sulfur or heated in an autoclave with 10 grams of carbon disulfide in slightly acid solution during 1 hour; the uncombined carbon disulfide is removed by distillation, and cc. of a per cent solution of potassium iodide. Hereafter the emulsion'is heated to 90 C. for about ti hour. The addition of potassium iodide serves for increasing the sensitiveness. After this treatment the emulsion is ready for being worked up.

ing to Example 1 with the difference that the silver nitrate is dissolved in water and 50 per cent of the ammonia which was necessary for dissolving the silver nitrate is added to Solutions 1 and 3 in the ratio 3:1.

The action of the substance which causes fog must of course be compensated after the desired and the density of the pictures made therewith are improved when at least a small amount of silver iodide is incorporated in the emulsion, for instance, 5 per cent or'less. Emulsions suitable for the process are also such as are obtainable by peptization of a silver bromide deposit in gelatin. Very good results are obtainable when adding to V the Solutions 1 and-3 in Example 1 a small quantity of ammonia. As already mentioned in Example 1 the operation should be carried out in an open vessel, however, I may likewise neutralize a certain amount of the ammonia by adding an acid. This quantity can be easily determined by experiment. As a rule at least 30 per cent of the added ammonia should be neutralized, but at least 10 per cent of ammonia should remain in the mixture until washing of the emulsion. Furthermore, it has proved advantageous to add only part of the whole quantity of gelatin to be used for the production of the emulsion in the emulsifying operation proper and to add the rest in form of dry gelatin while cooling the emulsion before washing. To the emulsions there may be applied, if desired, dyestuffs as usual in pho-' tography, forinstance, bleaching-out dyes, such as phenosafranine and fuchsineflor sensitizers or filter dyes.

In the annexed drawing there is shown the gradation curve of an emulsion produced according to my invention. The abscissa} are 'marked in the usual measure of log. it, while the ordinates denote blackenings'of the emulsion when developed for 5 minutes with standard developer according to the proposition of Luther, measured in the usual density units. The emulsion made according to the process described bleach out to a clearness of 0.8 density unit and below and even to 0.4 and below.

The invention is not limited to the above examples or to the specific details given therein. Many changes of detailswill occur to those skilled in the art without departing from the scope of the invention.

What I claim is:

1. The process of manufacturing photographic emulsion layers directly yielding positive pictures which comprises producing a strongly fogged silver halide emulsion by the addition of a substance which causes fog and bringing the fogged emulsion to strong solarization.

2. The process of manufacturing photographic emulsion layers directly yielding positive pictures which comprises incorporating in the silver halide gelatin emulsion a compound which causes fog and heating the emulsion to a temperature within the range of about 45 to 100 C. until the blackening corresponds with that of the apex of the gradation curve.

'ture for about hour at about 90 C., and then 3. The process of manufacturing photographic emulsion layers directly yielding positive pictures which comprises incorporating in the silver halide gelatin emulsion a compound selected from the group consisting of silver nitrate, ripening substances, a reducing agent and mixtures thereof and heating the emulsion to a temperature within the range of about to 100 C. until the blackening corresponds with that of the apex of the gradation curve.

4. The process of manufacturing photographic emulsion layers directly yielding positive pictures which comprises preparing a first solution containing gelatin, ammonium bromide, potassium iodide and water; a second solution containing silver nitrate, ammonia and water, and a third solution comprising gelatin, ammonium bromide, potassium iodide and water, mixing the first and the second solution after heating the same to about C. and keeping the mixture for about hour at about C., and then adding the third solution.

adding the third solution.

6. The process of manufacturing photographic emulsion layers directly yielding positive pictures which comprises preparing a first solution containing gelatin, a ripening substance, ammonium bromide, potassium iodide, ammonia and water, a second solution containing silver nitrate and water, a third solution containing gelatin,

ammonium bromide, potassium iodide and water, mixing the first and .the second solution after heating the same to about 80 C. and keeping the mixture for about hour at about 90 C., and then adding the third solution.

7. The process of manufacturing photographic.

iained by boiling 2.6 grams of gelatin with 0.2

gram of colloidal sulfur in slightly acid solution, and 5 cc. of a 10 per cent solution of potassium'iodide to 1 kilo of the molten emulsion and heating the emulsion to about 90 C; for about hour.

HANS ARENS. 

